Verify the given identities : (for this post the letter T will = angle theyta)
a) Sin 3T = 3 sinT - 4 sin^3T (hint 3T=2T+T)
b) cos 3T = 4cos^3T-3cosT
I used the trig identites I know to break them down, but I couldnt get it to the form of a and b. for example, for A I got this :
sin3T = sin(2T+T) = sin2t x cosT + cos2T x sinT =
But I get stuck at 3. Dont see how he gets 3sinT-4sin^3T as the answer. same problem with problem B. Can someone show me the light?
- (2sinT x cosT)cosT + (cos^2(T) - sin^2(t))sinT =
- 2sinTcosT^2 + sin(T)cos^2(T)-sin^3(T) =
- sin(T) (sin(T)cos^2(T) +cos^2(T)-sin^2(T))
Hey what trig identity did you use to change 3sinTcos^2T into 3sinT(1-sin^2T) ?
Originally Posted by Archie Meade
It's a very fundamental one, you'd need to remember it well
Originally Posted by frankinaround
(it comes from Pythagoras' Theorem).